JPH06205942A - Method for purifying waste combustion gas and catalyst used for the method - Google Patents

Abstract

PURPOSE:To provide a method for purifying waste combustion gas generated from lean burn system and a catalyst used for the method. CONSTITUTION:The waste combustion gas containing small quantity of a lower hydrocarbon, nitrogen oxides, carbon monoxide and a large quantity of oxygen is allowed to react in the presence of the catalyst made by allowing gallium to be carried (carrying quantity is 0.1-10wt.%) on a carrier made of ZSM-5 type zeorite or ferrierite type zeorite. If necessary, a small quantity of a lower hydrocarbon is newly added into the waste combustion gas, total quantity of the lower hydrocarbon contained in the waste combustion gas and the newly added lower hydrocarbon is a quantity required for reducing and purifying nitrogen oxides contained in the waste combustion gas. The lower hydrocarbon contained in the waste combustion gas is 1-4C lower hydrocarbon and the newly added hydrocarbon consists of at least one kind of methane, ethane and ethylene.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying combustion exhaust gas, and more particularly to a method for purifying combustion exhaust gas generated by a lean burn method and a catalyst used in the method.

[0002]

2. Description of the Related Art In recent years, attention has been paid to environmental problems worldwide, and not only mobile sources such as automobiles,
There is an urgent need to further remove nitrogen oxides, hydrocarbons, carbon monoxide, etc. from fixed sources such as cogeneration facilities.

At present, it is desirable to employ a lean burn method in order to suppress combustion efficiency, thermal efficiency or carbon dioxide emission. In that case, a small amount of lower hydrocarbons,
There will be nitrogen oxides, carbon monoxide and large amounts of oxygen.

Conventionally, a selective reduction denitration method by addition of ammonia or a purification method by a three-way catalyst has been adopted as a method for purifying gas combustion exhaust gas by removing a small amount of the above-mentioned lower hydrocarbons, particularly methane, nitrogen oxides and carbon monoxide. However, there is a problem that the ammonia method is very toxic for handling ammonia, and the three-way catalyst method is effective only under conditions where there is almost no oxygen at an air ratio of around 1.0. Has been done.

Japanese Unexamined Patent Publication No. 63-100919 discloses a method in which an exhaust gas discharged from an internal combustion engine of an automobile or the like containing nitrogen oxides is brought into contact with a copper catalyst in the presence of hydrocarbons in an oxidizing atmosphere. Although a method for removing nitrogen oxides in exhaust gas and a catalyst in which copper is supported on zeolite as a copper catalyst used in the method have been started, they are not in a satisfactory state.

Japanese Unexamined Patent Publication (Kokai) No. 2-265649 discloses a method for purifying exhaust gas discharged from an automobile or the like, which is capable of efficiently purifying NO _X , CO and hydrocarbons in an oxidizing atmosphere in which oxygen is excessively present. It has been disclosed, the only oxidation catalyst such as palladium can not be completely carried out the purification of NO _X, in order to purify NO _X, CO and hydrocarbons simultaneously, an oxidation catalyst, such as copper silicate catalyst and palladium It is merely taught that it is necessary to use a catalyst system consisting of a combination of Moreover, the above hydrocarbon is not specifically described.

Catalyst No. 32 No. 6. 1990, 430
Pp. 433 uses a copper ion-exchanged ZSM-5 zeolite catalyst to produce exhaust gas from diesel engines, lean burn gasoline engines, etc. in the presence of oxygen and hydrocarbons.
It has been reported that it is possible to efficiently reduce and remove nitrogen oxides in the exhaust gas by reacting in a temperature range of 00 to 400 ° C. However, the applicable reaction temperature range is narrow and satisfactory. Not in the right state.

The present invention is a method for purifying combustion exhaust gas generated by a lean combustion system, in which nitrogen oxide contained in the combustion exhaust gas is extremely high in selectivity over a wide reaction temperature range by using a specific catalyst. Can efficiently reduce and purify the lower hydrocarbons and carbon monoxide contained in the combustion exhaust gas, and the lower hydrocarbon newly added to the combustion exhaust gas as required at the same time. It is an object to provide the purification method and a catalyst used in the method.

[0009]

[Means for Solving the Problems] That is, the present invention is
A flue gas produced by a lean burn method, the flue gas containing a small amount of lower hydrocarbons, nitrogen oxides, carbon monoxide and a large amount of oxygen, is a carrier made of ZSM-5 type zeolite or ferrierite type zeolite. In the presence of a catalyst supporting gallium in the presence of a catalyst, a small amount of a lower hydrocarbon is newly added to the combustion exhaust gas if necessary, and a lower hydrocarbon contained in the combustion exhaust gas is necessary. The total amount of lower hydrocarbons newly added to the combustion exhaust gas according to the above is the amount necessary for reducing and purifying nitrogen oxides contained in the combustion exhaust gas, and the lower hydrocarbons contained in the combustion exhaust gas. hydrocarbon is C ₁ -C ₄ lower hydrocarbon, methane lower hydrocarbon newly added to the flue gas as required, it than with one least ethane and ethylene There is provided a catalyst used in said process comprising carrying gallium and ZSM-5 type zeolite or ferrierite-type zeolite consisting of the carrier; that purification method of the combustion exhaust gas characterized by.

In the present invention, the lean-burn method refers to raw materials such as city gas, LP gas, gasoline, light oil, and heavy oil,
It means a combustion method in which combustion is performed under the condition of excess air.

In the present invention, the combustion exhaust gas generated by the lean combustion system is generated by combustion under the condition of an air ratio of about 1 to 5, contains nitrogen, oxygen, water vapor and carbon dioxide as main components and contains a small amount of components. , Nitrogen oxides of 5000ppm or less, though it varies depending on the type of raw fuel, 2
C ₁ -C ₄ hydrocarbons up to% by volume and 5000 ppm
It contains the following carbon monoxide, respectively.

The catalyst of the present invention comprises gallium supported on a carrier composed of ZSM-5 type zeolite or ferrierite type zeolite.

The catalyst of the present invention can be obtained by supporting it on the above carrier by an ion exchange method using an aqueous solution of gallium salt such as gallium nitrate. The amount of gallium supported is 0.1 to 1
It is in the range of 0% by weight, preferably 1 to 5% by weight. If the supported amount is less than 0.1% by weight, sufficient activity cannot be obtained, and 1
When it exceeds 0% by weight, it is difficult to obtain the effect corresponding to the increased amount of gallium, which is not preferable.

The catalytic reaction in the method of the present invention is carried out at a reaction temperature of 200 to 700 using, for example, a fixed bed flow reactor.
C, preferably 300-600 C and contact time 0.5.
It is carried out under the condition of 0.025 g · s · cm ⁻³ .

In the catalytic reaction in the method of the present invention, the lower hydrocarbons present in the combustion exhaust gas are necessary for the reduction reaction of the nitric oxide present in the combustion exhaust gas, and when the content thereof is insufficient, the above-mentioned catalytic reaction is carried out. At the time of the reaction, it is necessary to newly add a fixed amount of at least one kind of lower hydrocarbon, for example, methane, ethane and ethylene, and the addition amount is usually within a range of 2% by volume or less.

In the catalytic reaction in the method of the present invention, the nitrogen oxide contained in the combustion exhaust gas is 300 to 600.
In a wide reaction temperature range of ℃, it is efficiently reduced and purified to nitrogen with extremely high selectivity, and lower hydrocarbons and carbon monoxide contained in combustion exhaust gas and newly added lower hydrocarbons are also efficiently treated. Purified.

[0017]

According to the present invention, there is provided a method for purifying combustion exhaust gas generated by a lean combustion system, in which a nitrogen oxide contained in the combustion exhaust gas is spread over a wide reaction temperature range by using a specific catalyst. Can be efficiently reduced / purified with an extremely high selectivity, and at the same time, the lower hydrocarbons and carbon monoxide contained in the combustion exhaust gas and the lower hydrocarbon newly added to the combustion exhaust gas can be efficiently added at the same time. There is provided the above-mentioned purification method capable of purifying and a catalyst used in the method.

[0018]

EXAMPLES The present invention will be described in more detail with reference to production examples, examples and comparative examples.

Production Example of Ga-ZSM-5 (92) Catalyst
(Production Example 1) In 2.4 liters of 1 mol / 1, NH ₄ NO ₃ aqueous solution (manufactured by Kanto Chemical Co., Inc., JIS special grade NH ₄ NO ₃ ) at 80 ° C., HSZ-820NAA (ZS manufactured by Tosoh Corporation) was used.
40 g of M-5) was immersed in the mixture for 3 hours, stirred, filtered, and washed with 2 liters of pure water. After repeating this operation 6 times, after further washing with 2 liters of pure water, 110 ° C., 1
After drying for 2 hours, the base material of the catalyst according to the present invention (NH ₄ -Z
SM-5) was prepared. Continued Ga (NO ₃ ) at room temperature
₃・ nH ₂ O (Mitsuwa Chemical Co., Ltd.) 0.75g
Was added to 300 ml of pure water to prepare the prepared NH
_4- ZSM-5, 5g soaked, stirred, bath temperature 95 ℃
After keeping this state under heating for 24 hours under reflux, it is separated by filtration,
It was washed with 2 liters of pure water. Next, 110 ° C,
After drying for 12 hours, it was calcined in air at 500 ° C. for 3 hours to prepare a catalyst (Ga-ZSM-5) according to the present invention.
The amount of Ga carried in the catalyst was 2.4 wt-% (3 Ga).
/ Al × 100 = 92). SiO ₂ / Al ₂ O ₃ molar ratio of ZSM-5 zeolite is 23.3.

Production Example of Cu-ZSM-5 Catalyst (Production Example
2) 0.01 mol / 1, 1 liter of NaNO ₃ aqueous solution (Kanto Chemical Co., Inc., JIS special grade NaNO ₃ used),
HSZ-820NAA (ZSM-5 manufactured by Tosoh Corporation)
Na-ZSM-5 was prepared by washing 15 g and further washing with pure water and 2 liters. Then, a 0.01 mol / 1 (CH ₃ COO) ₂ Cu aqueous solution at room temperature (manufactured by Wako Pure Chemical Industries, Ltd., special grade (CH ₃ COO) ₂ C)
u · H ₂ O) 1 liter, Na-ZSM-5, 1
5 g was immersed for 12 hours, stirred, filtered, and washed with 2 liters of pure water. After repeating this operation once, it was further washed with 2 liters of pure water, dried at 110 ° C. for 12 hours, and then calcined in air at 500 ° C. for 3 hours to obtain a comparative catalyst (Cu-ZSM-5). Prepared. In addition, Cu in the catalyst
Is 3.9 wt-% (2Cu / Al × 100 = 1
11).

Production Example of H-ZSM-5 Catalyst (Production Example 3) NH ₄ -ZSM-5 is prepared in the same manner as Ga-ZSM-5. Then, the catalyst for comparison (H-ZSM-5) was prepared by firing in air at 500 ° C. for 3 hours.

Production Example of Ga-Ferrierite Catalyst (Production
Example 4) 1.8 mol of a 1 mol / 1 NH ₄ NO ₃ aqueous solution (Kanto Chemical Co., Inc., using JIS special grade NH ₄ NO ₃ ) at 80 ° C. was added with 3 g of TSZ-710KOA (Ferrierite manufactured by Tosoh Corporation). After soaking and stirring for 2 hours, filter and separate
It was washed with 1 liter of pure water. After repeating this operation 6 times, after further washing with 2 liters of pure water, 110
After being dried at ℃ for 12 hours, the base material of the catalyst of the present invention (NH
₄ -ferrierite) was prepared. Continued Ga at room temperature
(NO ₃ ) ₃・ nH ₂ O (manufactured by Mitsuwa Chemical Co., Ltd.)
The prepared NH ₄ -ferrierite (3.3 g) was immersed in an aqueous solution prepared by dissolving 0.56 g in 240 ml of pure water, stirred, heated to 95 ° C. and kept under reflux for 24 hours. , Filtered and washed with 2 liters of pure water. Next, after drying at 110 ° C. for 12 hours, it is dried in air at 50
The catalyst (Ga-ferrierite) according to the present invention was prepared by calcining at 0 ° C. for 3 hours. The amount of Ga carried in the catalyst was 3.0 wt-% (3Ga / Al × 100 = 91). Ferrierite-type zeolite SiO ₂ / Al ₂
The O ₃ molar ratio is 17.8.

Production Example of Ga-ZSM-5 (276) Catalyst
(Production Example 5) NH ₄ prepared in the same manner as in Production Example 1 in an aqueous solution prepared by dissolving 2 g of Ga (NO ₃ ) ₃ · nH ₂ O (manufactured by Mitsuwa Chemical Co., Ltd. ) at room temperature in 300 ml of pure water. -ZSM-
Soak and stir 5, 5g, raise the bath temperature to 95 ° C, 24
After maintaining this state under reflux for an hour, it was filtered and washed with 2 liters of pure water. Next, after drying at 110 ° C. for 12 hours, it was calcined in air at 500 ° C. for 3 hours to prepare a catalyst (Ga-ZSM-5 (276)) according to the present invention. The amount of Ga carried in the catalyst was 6 wt-% (3 Ga / Al.
× 100 = 276).

Example 1 Using a normal pressure fixed bed flow reactor, as a typical example of combustion exhaust gas, 1000 ppm of nitric oxide and 1000 p of methane
pm, oxygen 10% by volume and the balance helium in the presence of 0.5 g of the Ga-ZSM-5 catalyst of Production Example 1 at a reaction temperature of 300 to 600 ° C and a total flow rate of 100 cc.
The reaction was carried out under the condition of / min. With NO _X analyzer Gas Chromatograph and a chemiluminescence for the analysis of the reaction gas. Table 1 shows the conversion rates of nitric oxide to nitrogen and methane.

Examples 2 to 4 and Comparative Examples 1 to 4 In place of the Ga-ZSM-5 (92) catalyst of Example 1, the catalysts shown in Table 1 were used, and 1000 ppm of ethane or 250 pp of ethylene was used instead of 1000 ppm of methane.
The same experiment as in Example 1 was performed except that m was used. The results obtained are shown in Table 1.

Example 5 The same experiment as in Example 3 was conducted except that the oxygen content was 5% by volume. The results obtained are shown in Table 1.

Example 6 The same experiment as in Example 3 was conducted except that the oxygen content was 2% by volume. The results obtained are shown in Table 1.

Example 7 The same experiment as in Example 3 was conducted except that the amount of gallium supported was 6% by weight. The results obtained are shown in Table 1.

[0029]

[Table 1]

Example 8 Example 3 under the same conditions as in Example 3 except that the catalyst amount was changed in the range of 0.05 to 0.5 g and the contact time was changed.
At 500 ° C., at which the maximum activity was shown in Table 2, the effect of the contact time shown in Table 2 on the conversion rate (%) of NO to N ₂ was conducted. The obtained results are shown in Table 2.

Comparative Example 4 Except that the experiment was conducted under the condition of 300 ° C., which showed the highest activity in Comparative Example 4, using the Cu-ZSM-5 (111) catalyst.
An experiment similar to that in Example 8 was performed. Table 2 shows the obtained results.
Shown in.

[0032]

[Table 2]

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[Procedure amendment]

[Submission date] April 13, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction content]

The present invention is a method for purifying combustion exhaust gas generated by a lean combustion system, in which nitrogen oxide contained in the combustion exhaust gas is extremely high in selectivity over a wide reaction temperature range by using a specific catalyst. in low contained in combustion flue gas it is possible to efficiently reduced and purified
An object of the present invention is to provide the purification method and the catalyst used for the purification method, which can simultaneously efficiently purify high-grade hydrocarbons and lower hydrocarbons newly added to combustion exhaust gas as needed.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction content]

In the catalytic reaction in the method of the present invention, the nitrogen oxide contained in the combustion exhaust gas is 300 to 600.
In a wide reaction temperature range of ℃, it is efficiently reduced and purified to nitrogen with extremely high selectivity, and lower hydrocarbons contained in combustion exhaust gas and newly added lower hydrocarbons are also efficiently purified.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction content]

[0017]

According to the present invention, there is provided a method for purifying combustion exhaust gas generated by a lean combustion system, in which a nitrogen oxide contained in the combustion exhaust gas is spread over a wide reaction temperature range by using a specific catalyst. It is possible to efficiently reduce and purify with extremely high selectivity and simultaneously purify simultaneously lower hydrocarbons contained in the combustion exhaust gas and lower hydrocarbons newly added to the combustion exhaust gas as needed. A possible purification method and a catalyst used in the method are provided.

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Claims (7)

[Claims] 1. A flue gas produced by a lean burn method, the flue gas containing a small amount of lower hydrocarbons, nitrogen oxides, carbon monoxide and a large amount of oxygen is converted into ZSM.
-5 type zeolite or ferrierite type zeolite is made to carry out a catalytic reaction in the presence of a catalyst supporting gallium on a carrier, and a small amount of a lower hydrocarbon is newly added to the combustion exhaust gas, The total amount of lower hydrocarbons contained in the combustion exhaust gas and lower hydrocarbons newly added to the combustion exhaust gas as necessary is necessary for reducing / purifying nitrogen oxides contained in the combustion exhaust gas. The lower hydrocarbon contained in the combustion exhaust gas is C
₁ -C ₄ a lower hydrocarbon, method for purifying combustion exhaust gas, characterized in that lower hydrocarbon newly added to the flue gas as required is formed of one at least of methane, ethane and ethylene. 2. The method according to claim 1, wherein the amount of gallium supported is in the range of 0.1 to 10% by weight. 3. The method according to claim 1, wherein the lower hydrocarbon content in the combustion exhaust gas is about 2% by volume or less. 4. The method of claim 1, wherein the newly added lower hydrocarbon is in the range of about 2% by volume or less. 5. The method according to claim 1, wherein the catalytic reaction is carried out at a temperature of 300 to 600 ° C. 6. The catalyst used in any one of claims 1 to 5, wherein gallium is supported on a carrier composed of ZSM-5 type zeolite or ferrierite type zeolite. 7. The catalyst according to claim 6, wherein the ZSM-5 type zeolite or the ferrierite type zeolite has a SiO ₂ / A1 ₂ O ₃ molar ratio in the range of 10 to 200.